This invention relates to reflector lamps and, in particular, to blown glass reflector lamps.
Among the many lamp characteristics involved in the choice of a lamp for a particular application, PAR (Parabolic Aluminized Reflector) lamps are specified when light control is paramount. As known in the art, these lamps are made from a pressed glass lens and reflector which must be sealed together. Compared to lamps made from blown glass bulbs, PAR lamps are heavy, costly, and difficult to make at high production rates.
Reflector lamps of the prior art made from a blown glass bulb, while lower in cost, have poorer light control.
Because of the lens in PAR lamps or the shallow bulb with consequent poorer light control of reflector lamps, directed light lamps of the prior art are characterized by high brightness (face luminance) from nadir through most normal viewing angles, requiring external shielding or suitably designed luminaires to reduce the glare. Such shielding reduces the illumination provided by the lamp since light off-axis more than a predetermined amount is absorbed by the shielding. As understood by those in the art, "brightness" refers to the appearance of the lamp when the lamp is viewed directly and is the term used for face luminance. Except for certain decorative applications, lamps are used for seeing, i.e., for their ability to illuminate where illumination is the density of luminous flux upon a surface. The ideal directed light source has the seemingly contrary characteristics of producing high illumination and having zero brightness off-axis, or out of the desired cone of light.
In general, lamps of the prior art have not come very close to this ideal. A lamp having an approximately ellipsoidal reflector, known in the prior art, was identical to, except for the shape of the reflector, the PAR lamps noted above, i.e., heavy, costly, difficult to make, and using a lens to control light distribution. An elliptical lamp is disclosed in U.S. Pat. No. 1,981,329, although it is not disclosed how the lamp is made; i.e., it is not disclosed whether the lamp is blown or molded or whether glare is controlled.